Control mechanism for hydraulic transmissions



May 6, 1947.

W. R. TUCKER CONTROL vIECZHARISII FOR HYDRAULIC VTRANSIISSIOHS 2 Sheets-Shut l May 6, 1947. w. R. TUCKER 2,420,155

CONTROL IECHANISII FOR HYDRAULIC TRANSIISSIONS Filed lay s1, 1941. 2 sheets-sheet 2V Patented May 6, 1947 CONTROL Warren R. Tucker,

MECHANISM FOR HYDRAULIC TRANSMISSIONS- u Oakwood, Ohio,

assignor yto The Hydraulic Development Corporatiomulnvc.,

Wilmington, Del., a co rporation of Delaware Application May 31, 1941', Serial No. 396,033 6 Claims. (Cl. (iO-53) This invention relates to hydraulic transmissions wherein the motor and pump elements are variable in their displacement, 'and more particularly relates to means for controlling the speed of output developed by the transmission and the torque obtained from the transmission.

An object of the invention is to provide a hydraulic transmission which will produce a substantially constant torque transmitted by the shaft thereof.

Another object of the invention is to control a hydraulic transmission in response to the torque to vary the displacement of the'mechanisms of the transmission to maintain substantially constant torque transmission thereof.

Another object a hydraulic transmission cally reduce its delivery in response imposed upon the transmission.

It is another object of the a hydraulic transmission which will reduce its speed as the torque load tends to increase thereby maintaining the load on the driving apparatus substantially constan Another object of a hydraulic transmission which will prevent overloading of the driving apparatus.

Itis another object of the invention to provide a hydraulic transmission the speed of which can of the invention is to provide which will automatito the load be varied manually or automatically, and has mechanism which will automatically prevent overloading of the driving apparatus regardless of the speed which is imposed upon the transmission by the speed changing mechanism.

It is another object of the invention to provide a hydraulic transmission which will automatically shift the when the load imposed upon thev transmission rises above a safe limit.

It isanother object o f the invention to provide a hydraulic transmission wherein vane pumps are used as the pump and motor thereof, and wherein a pilot pump is used for delivering pressure to the vanes to maintain them in operating position, Which pilot pressure becomes a safety control when undue pressure within the transmission.

It is another object of the invention to provide a transmission in accordance with the foregoing is developed by the drive shaft,

inventionto provide the invention is to provide pumping mechanism to neutral object wherein tor which are variable in object wherein thepilptpump also delivers fluid to serve thefmotor f of the pumpingmechanism. l

It is another object ofthe invention to provide a hydraulic transmissionwiierein the pump and motor are both variable .'a's'to their displacement, and wherein mechanism is provided yfor automatically changing thel displacement of the pump or motor for altering the speed output of the transmission.

Another object'of the invention is to provide in accordance with the previous the apparatus for controlling the of the pump or motor is actuated a transmission displacement in response transmission for maintaining substantially constant torque development at the output of the I transmission.

It is another object of the invention to provide a hydraulic transmission wherein the displacement of the pump and motor is variable having means for manually controlling the speed output of the transmission and means for automatically controlling the load imposed upon the driving apparatus by the transmission.. r

It is another object of the invention to provide a hydraulic transmission having a pump and modisplacement and means providing a safety control of maximum pressure developed by the transmission.

Further objects and advantages will become apparent from the drawings and the following description.

In the drawings:

Figure 1 is a longitudinal cross-sectional view of a hydraulic transmission which can be used -in combination with the features of this invention.

Figure 2 is a transverse cross-sectional view taken along line 2--2 of Figure 1.A

Figure 3 is a diagrammatic representation of a transmission having a pilot pump for serving A 'someor changing the eccentricityto pressure developed Within the 1 a hydraulic transmission incorporating control features of this invention.

Figure 6 is a -diagrammatic representation of a hydraulic transmission incorporating control features of this invention in a modified arrangement. f

This invention relates to hydraulic transmissions wherein the eccentricity of the pumping unit and the motor unit, either or both, is variable, whereby the displacement of either the' Vmotor or the pumping unit is changed to control the speed ofoutput of the transmission. Automatic control mechanisms are associated with the motor and pumping units to regulate the changes in displacement in accordance with certain pressure conditions within the transmission to produce a transmission which is responsive to the load conditions imposed upon the transmission and thereby establishl a substantially oonstant torque output. The control mechanisms can also function as safety devices to unload the primary source of power should the load imposed upon the transmission become too great to be handled by the primary source of power. The control system of this invention is applicable to .any hydraulic transmission wherein the pump and motor units have variable displacements and, while a particular transmission will be hereinafter described which in combination with other features of the invention has special functions, it is to Vbe understood that the structural arrangement of the transmission can be altered without departing from the spirit of the control features of the invention. The particular transmission described hereinafter is associated with the pilot pump which establishes substantially constant pressure to the vanes of the vane type pumps used as the motor and power unit of the transmission. The constant pressure supplied by the pilot pump provides a feature of safety control ln a vane type pump which is somewhat special to a mechanism wherein hydraulic pressure is used to maintain the operative position of the pumping devices whether they be vanes or pistons. The other control features of the invention Vhowever are applicable to any hydraulic transmission having variable displacement of the pump and motor units.

In this invention the hydraulic transmission described herein consists of a pair of vane pumps which are structurally identical.V 'I'he power or pumping unit only will be referred to in the following description but the elements of like character of the motor unit will be identified by the same numeral but with the suffix a.

The vane pump unit consists of a casing I having a work chamber I I and a liquid storage chamber I2. The casing I 0 of the pump unit 9 and the casing I0a of the motor unit 9a are separated by a partition I3 within which there is mounted a stub shaft I4 which extends on both sides of the partition I3. The casings IIJ and Illa are secured to the partition I3 by suitable bolts to provide a unit casing for the motor 9a and pump unit 9. The partition I3 has an opening I5 therein for interconnecting the reservoir compartments I2 and I2a for storage of hydraulic liquid therein and to permit circulation of the flow of liquid from the motor unit in the working compartment Ila to the pump unit in the working compartment I I.

The vane pump unit consists of a cylinder I6 of substantially rectangular form having a cylindrical bore I1 therein which provides tile cylinder wall for the pumping unit. The cylinder block I6 is positioned between parallel planar faces I8 and I8 provided in the pump casing III. The cylinder I6 is adapted to reciprocate with respect to the casing, on faces I8 and I9 provided in the pump casing I 0, under control of suitable mechanism which is hereinafter described.

A rotor 20 is positioned within the cylinder bore f I I and is consequently mounted upon the stub shaft I4 by means of the needle bearings 2 I. End closure plates 22 and 23 are positioned adjacent opposite end faces of the rotor 20, which end plates are in engagement with the planar faces 24 and 25 of the cylinder I6. A plurality of `bolts 26 secure the end plates 22 and 23 and the rotor 20 together as a unit assembly.

The rotor 20 is provided with a ,plurality of radial slots 2l, each of which slots is adapted sto. carry a vane 28. Rotation of the vanes within" the cylindrical bore I1 produces a flow of liquid between the passages 28 and 30 provided in the cylinder I6, whereby fluid is circulated by the pump to or from the'reservoir I2 and is conducted to or taken from the passage 3| provided in the casing I0 in accordance with the eccentricity of the cylinder with respect to the rotor. If the eccentricity of the cylinder is as shown in Figure 2 the flow through the pump unit will be in one direction, whereas, if the eccentricity is 180 opposite that shown in Figure 2, the flow of uid through the pump will be in the opposite direction while the rotor rotation remains in the same direction as before.

The rotor 20 has a reduced diameter shaft 32 extending therefrom which carries a tapered roller bearing 33 the inner race 34 of which is carried upon the shaft 32 while the outer race 35 is carried within a recess .36 provided in the end wall of the casing I0. An externally threaded plug 31 is in threaded engagement with a threaded opening 38 provided in the end wall of the casing I0 and is in engagement with the race 35 of the roller bearing 33 for applying pressure through the roller bearing 33 upon the pump assembly to urge'the same in a. leftward direction as viewed in Figure l and thereby retain the end closure plate 22 in engagement with the annular boss 38 provided upon the face of the partition I3. A locking plug 40 is also in engagement with the threaded opening 38 for securing the plug 31 in position.

The reduced diameter shaft 32 has a reduced diameter shaft 42 integral therewith which extends through the opening 43 provided in the plugs 31 and 40 in the end wall of the casing I Il. The shaft 42 is connected to a suitable driving mechanism which operates the transmission,V

while the shaft 42a is connected to a mechanism driven by the transmission. A packing gland 4I is provided between the shaft 42 and the plugs 31 and 4II.

A pilot pump 45 which may be of the common gear type is carried upon the shaft 42 and has one gear 46 thereof driven by the shaft 42 through means of a suitable key 4l. A gear 48 is carried.

upon a stub shaft 48 and is in meshing relationship with the gear 46. Such a gear pump is well known in the ari; and it is not believed that further description is necessary. 'I'he pilot pump .45 is secured to the casing I0 by means of suitable bolts 50.

The inlet side of the pilot pump 45 is conand to a conduit 53 which is connected to a, tting 54 providedin the partition I3.

provided in the partition I3 and extendsfrom the fitting `5t to a transverse passage 56 provided in the partition I3. The transverse passage 56 is in communication with an annular groove 51 provided in the closure plate 22. iA second annular groove 58 is provided in the opposite face of the closure plate 22 and is in communication with a space 59 provided beneath the varies 28 within the rotor 20. A passage 60 connects the annular groove 51 with the annular groove 58 to conduct liquid from the passages 55 and 56 to the under side of the varies 28 when the pilot pump is delivering uid through the conduit 53.

When the hydraulic transmission is operating the pilot pump 45 withdraws iiuid from the reservoir I2 through the tting 52 and the conduit 5I and delivers the same through the conduit 53 to the under side of the vanes. The pressure of the liquid delivered by the pilot pump 45 is maintained relatively constant through means of a pressure relief valve 6I positioned in the by-pass line 62 interconnecting the conduit 53 with the fluid reservoir I2 through means of the iitting 63. The pressure relief valve 6I opens when the pressure in the conduit 53 reaches a predetermined level to by-pass all excess fluid and thus maintain pressure in the conduit 53 substantially constant. with an adjusting mechanism 64 for regulating the pressure at which the telve 6I will open, thus providing means to control the pressure apfplied to the under side of the vanes 28. y

With a substantially constant pressure applied to the under side of the vanes 28 the maximum pressure developed within the` pumping mechanism is controlled to prevent the development of undue high pressure. The passages 3Ir andr 3Ia receive the liquid discharged by the pump 9 within the work chamber II. The pressure within the passages 3l and 3Ia exerts a force uponthe outer ends of the vanes 28 attempting to move the vane inwardly against the pressure existing in the space 59 below the vane 28. When the pressure in the passages 3l and3la reaches a certain predetermined level the force exerted upon the outer ends of the vanes 28 will move the vanes inwardly against the pressure in the space 59. The pressure at which this will occur depends upon the pressure existing within the space 59`and the relative surface areas exposed to the pressures above and below the vanes 26. The constant pressure applied to the under side of the Vanes 28 thus becomes means for regulating the maximum pres- A passage 55 is sure developed within the pumping mechanisms of the transmission` and thus becomes a safety control to prevent over-loading of the transmission should the power shaftv42a be stalled or be caused to direct aheavier load upon the motor of the transmission than the pumping mechanism is designed to carry.

The pump 9 and the motor 9a are each .provided with a mechanism for shifting the cylinders I6 and IGa respectively with respect to the rotors 28 and 20a, whereby the displacement within the cylinder bores I1 and Ila are varied thereby alteringthe speed output lof the motor shaft 42a. The shifting mechanisms for the cylinders I6 and I6a are adapted to be manually controlled for altering the speed output of the transmission, or may be automatically controlled for regulating Vthe torque output of the pump or controllingvthe output speed thereof.

Thepressure reliefvalve 6I is provided 'direction toward neutral position.

' ing end portion 83 The control mechanisms' are identical in structure and therefore a description of the control mechanism associated with the pump unit 9 will suicefor `the control mechanism of the motor unit 9a..,

The controldevice 65 for the pump unit 9 consists of a spring 66 positioned within the storage chamber I2 having one end thereof carried-by anladjustable abutment 61 and the opposite end carried by a stud 68 in engagement with the `end ofa lever 68. The lever 69 is po# sitioned withinl. recess 10 provided inthecasing I6 and vis ,pivoted uponthe pin 1I carried by `a boss 12. The end orV the lever k69 opposite the end in engagement with the spring 66 engagesy a pin 13yslidably positioned within a bore 14 provided in thek wall yor" they work chamber II.' Thek inner end of the pin 13 rengages the end wall 15 of the cylinder I6. The spring 66 urges the lower end of the lever 69 in a leftward direction as f viewed Vin Figure 2 and thereby urges .the upper end of the lever 69 in arightward direction for which has a threaded portion 11 in threaded engagement with the threaded cpening 18 provided in the wall ofthe casing I0. The pin 16 is provided with a packing gland 19 and a packing nut for sealing the opening pin I6 varies the compression of the` spring 66 and therebyl alters thepressure developedw'lthin n the pump capable of overcoming the spring compression to move the cylinder `I6 in a leftward A control piston sl is sudebie within a bore 82 provided in the casing `III and-has a protrud- 84` of the cylinder I6. which wall 84 is opposite to the wall 15 so that movement of the control piston 8l opposes movement of the springk66 through the pin'-13.. l The control piston 8I is moved either manually or in response to pressure developed lwithin the pump 9 to control the degree of eccentricity of the cylinder I6 with respect to the-rotor 20.

A iitting 85 carries a stem 86 in threaded en'- gagement therewith within the threaded opening 81. The inner end of the stern 86 is adapted to be placed in engagement with the control piston Y 8l, while the outer end of the stem 86, carries a wheel 88 for rotating the same to vary' the position'of the inner end of the stem'86 and thus the position of the control piston 8|. A packing gland 89 and a packing nutl 9|) seals -the stem 86 to prevent flow of iiuid fromwithin the pumping unit.

vTheL iitting 85 has a passage 9| which is'adapted to be connected by meansof a suitable conduit to the discharge passage 3I ofjthepump 9v for conducting liquid `under pressurejpto the chamber 92 provided between the fitting 85 and the casing IU. The piston 8l is freely4 reciprocable within the bore 82 so that vwhen pressure within thechamber1'92 increases sufficiently, the force applied by the kpiston 8| in a leftward direction will overcome the action ofthe spring 66 to move the cylinder I6 toward neutral position. The pressure at which the cylinder I6 will move toward neutral is controlled by the spring 66 and can be adjusted over awide range to produce l any desired torque effect Aupon the motor 9d,

18.- Rotation of` the f in engagement Withthe wall t which pressure is limited only by the capacity of the mechanism driving the pump 9. .Figure disclosed diagrammatically 'a' transmission wherein the motor 9a` andthe pump 9 are interconnected in circuit flow relationship by conduits 93 and 94.1' Theisprings 69 and 69a urge the cylinders of the motor and pump toward full stroke position while the vadjustingstems 96 and 96a acting through pistons liiand Bla oppose the action ofthe springs 69 and 66d tending to move the cylinders of the motor and pump toward neutral. A conduit l95' interconnectsA the discharge conduit '99 of the pump'9 with the chamber 92 provided in the adjusting device 85. The springs 66 and 99a are Vof sumcient. strength to normally retain the. motor and pump on full stroke position at all times. The cylinder of the pump 9 will be' moved toward neutral position when pressure in the conduits 94 and 95 rises above apredetermined level as determined by the spring 6B. The "shaft 42 of the pump 9 is connected to an electric motor 91 while th'e shaft 42a of the motor 9a is connected to a mechanism driven by the transmission. Under normal operating conditions the cylinder of the motor 9a is .set in a predetermined eccentric position with respect to the rotor thereof by means of the adjusting screw 86a.

Vmotor-and pick upI .a lessened load.

condition upon the motor has been relieved after which the pump will continuek operation of the Such' a safety control featureon a hydraulic transmissionis advantageous where the load conditions conditions the compression of the spring 96 will be adjusted so that the pressure developed within the pump, while considerably less than the lmaximum pressure capable of being transmitted by the pump, will nevertheless be equal to the pressure required to developthe desired torque bythe motor shaft 12a at the particular speed of operation thereof. A"When they spring 69 is functioning Aas a torque control the maximum output of the power mechanismy 91 is not used.

v To obtain the desired'speed and pressure relai The spring 89a `maintains the position of the cylinder of the motor with respect f v to the rotorywhile the screw 99a limits the action of the spring 69a to regulate the relativeposi.-

tions of the cylinder and rotor. The pump 9 is also set to a predetermined-eccentric position to obtain the desired delivery from the pump to themotor 9a toproduce the desired speed delivery through the shaft 42a.Y The-displacements -oi `the motor'and pump'can thus be varied over a.v

considerablerange and thereby /obtain a wide rangeof shaft speedsoi the output shaftv 92a.` I

The electric motor-",or any other propulsion apparatus for driving the pump 9, has a predetermined operating Vcapacity .above whichthe i the compression of the spring-69 can be set by power mechanism will stall. 'The-'spring 99 ofthe pump 9 can be used to-produce` two -diiierent` the adjusting screw 19 to permit pressure to build up within the pump 9V'to a point at which'the full Y capacity of the power mechanism or electric motor 91is utilized andabove which the power mechanism would stall. When this'pressure has been reached by the pump`9, the'discharge pres-i sure will be transmitted from the discharge conduit 94 through the conduit 95 to thespace 92 of the control mechanism 95. .The pressure within the chamber 92-will move the piston 9| inwardly and thereby shift the cylinder 68 with respect to the motor 20 to neutral thereby halting the delivery of liquid bythe pump 9; 'i Sumcient liquid however will be continued to be delivered by'the pump 9to maintain the lpressure tionship between the motor and the pump the adjustingmechanisms 96"and 96a are properly positioned. l

. When the spring 69 is functioning as a torque control the pump 9 will be operating at a pressure less than its maximum so that any variation in load upon themotor shaft 42a reflects directly upon the pressure developed vby the pump 9. Any increaser of load 'upon the shaft 42a has the effect of retarding the rotation of the shaft 42a in the normal direction.' yof rotation so that it takes a greater pressure in the motor with a constant volumedelivery to carry the load if the rotation .of the shaft 42 is not to slow down. However, if

thevtorque transmitted bythe motor shaft 42a is to remainsubstantially constant, the pressure apy plied on theymotor 9a by the pump 9 must remain substantially constant. Thus,l `when the motor tends to force 'the pressure upwardly in it andthe pump, th'e pump is shifted toward neutral position `to reduce the ydelivery therefrom and yet hold f duce the delivery thereof until thepressure in the conduits 94 and 95 is vequal to the resistance -of the spring 66. The balance of opposing forces obtained by the spring 66 and the pressure within Athe chamber V`92 of the adjusting device 95 maintains a relatively, constant pressure of delivery within the conduits 99 and 95, increasedonly by developed within Vthe conduit 94 for transmission l `to the motor 9a,fwhereby the motorwill apply maximum torque effort upon the drive shaft of the motor for driving the apparatus driven by the motor shaft 42a. The yspring 9|. thus becomes a safety control for the transmission. 4fte-- gardless of the load imposed upon the `motor la l the added resistanceof the spring 68 upon increased compression thereof, regardless of the Y volume delivered by the pump. When the vol the pump 9 cannot produce a pressure.abovethe"v Y predetermined maximum pressure as determined by the' spring 66 so that even thoush the motor should stall due to theload condition the pump* will automatically be yshifted toneutral and even. though it continues nperation. there` will be 'no delivery of liquid to ti'lv,lillmttufiuntil thc 4load urne delivered by the pump 9 is reduced andv therefore the speed of operation ofthe motor is reduced, with substantially the same pressure present inthe motor, the torque transmittedlby "the'motor shaft 42a will remain substantially 701' constant but at ayreduced speed. It is thus seen that the control mechanism of the transmission of this invention can maintain the torque transmitted bythe d'rive shaft thereof substantially constant with a slight sacrificeof speed of operation.

While the liquid pressure for operating the control piston 8| has been described as being ya pressure transmitted from the discharge conduit of the pump 9, it is also to be understood that the internal lworking pressure of the pump can also be used to provide the control tending to move the pump to neutral position. This is particu# larly true of the vane type pumps. If the internal workingl pressure of the pump is used to shift the cylinder to neutral position upon development of a predetermined pressure th'en the control piston 8| can be dispensed with. However, the manual control for pre-setting the displacement relationship of the motor and pump will be retained to control the speed regulation of the output shaft 42a and the motor 9a. It is to be understood that if the internal pressure developed by the pump is used for shifting the cylinder that the spring 66a of the motor 9a will be suiciently strong to prevent shifting of the motor cylinder at any time to prevent the motor 9a from tending to increase its speed by shifting oi.' the cylinder thereof toward neutral position. The spring 66 could thus be considerably lighter than the spring 66a and could control the operation of the pump 9 in the same manner as heretofore described depending lupon the degree of compression of the spring and whether it is t be used only as a safety 4control or as a substantially constant torque control.

The manual control heretofore described of the pump and motor, 9 and 9a, is satisfactory on all small hydraulic transmissions. However, when the transmissions are of relatively large size, or when the pressure produced in the'transmission is of a relatively high order difficulty is encountered in shifting the cylinder purely by manual means. It is therefore desirable under certain conditions to provide a servomotor for shifting the cylinders of the pump or motor. f. A somewhat simplified form of servomotor |00 is disclosed in Figure 4, The pilot pump 45 is adapted to supply iiuid pressure to the servomotor |00. The discharge side of the pilot pump 45 is connected to the servomotor |00 by means of a conduit 10| which is a branch line of conduit 53. The discharge side of the servomotor |00 is connected by1 means of a conduit |02 to the fitting |33v for returning liquid to the liquid storage chamber |2 within the casing I0.

The servomotor |00 consists of a body |03 having two cylinder bores alignment of which the cylinder bore |05 is the larger. A step` diameter piston |06 is positioned within the cylinder bores |04 and |05 and is adapted to be slidable therein. The piston |06 is provided with an axially extending portion |01 in engagement with the cylinder of leither the pump 9 or the motor 9a. It is to be understood of course that a separate servomotor is provided for the motor and pump. A piston |08 is carried within a cylinder bore |09 provided within the piston |06. The piston |08 is connected to a control rod ||0 which extends exteriorly of the servomotor |00 and is connected either toa manual control device or an automatic control device. A spring is carried within a bore ||'2 pro- `vided within the piston |06 for normally urging the piston |08 in the rightward direction.

The conduit |0| is in communication with an annular groove ||3 which in n through -a transverse passage |4 with the interior of the cylinder bore |09. An annular recess ||5 is provided around the cylinder bore |09 and communicates through a longitudinal passage ||6 with a. space ||1 provided at the righthand end of the piston |06.

' annular. groove |8 The return conduit |02 communicates withan.l 4

which communicates with the interior ofthe cylinder bore IUBbYnanyof, passage H9.

The piston |08 normally spans the annular -f 4 l 'that hydraulic i :1 v

the annular groove H8 urges the i groove I5 and the passage ||4so pressure within piston |06 in-a rightwardfdirection againstytherod f of the piston |06. When the cylinderofthe"A e: with'which the'servomotor is associated is to' be` shifted to neutral with respect to the rotor-the control ro-d ||0 is moved in a leftward direction whereby the piston hand side of the piston los through 'the cylinder bore |09. The piston |06 then moves in a leitward direction due to v the chamber l||`| until the passage ||4 is again closed by means of the end of the piston |08.

A When the eccentricity oi the cylinderis toy be' increased with respect to the rotor of either the pump or motor the control I0 is moved in a rightward direction whereby the liquid under pressure within the annulargroove ||3 is transmitted to the reduced diameter area |90. on the left-hand end of the larger diameter portion of the piston |06. When the piston |08 uncovers the left-hand edge of the annular groove ||5 the chamber 1s in communication withthe return vconduit |||2v through means of the passage IIB, the groove I5 and the passage kH9 whereby liquid can now from the chamber when the piston |06 is moved in a rightward direction until theletl hand edge of the annular groove ||5 is closed by |04 and |05 in coaxial turn communicates means of the piston |08.

The pilot pump 45 thus produces a second funci tion of operation upon the hydraulicv transmission.

In order to operate the servomotor automatically 1n response to load conditions imposed upon the motor 9a of the transmission it is necessary that a pressure control be associated with the servomotor which is responsive to the pressure existing within the discharge conduit of the pump 9. Figure 6 is a diagrammatic representation of a hydraulic transmission having' a pilot pump for serving the servomotorsof the pump and motor of the transmission, and wherein a pressure control is provided for the servomotor4 on the pump of the transmission for controlling the same in response to the pressure yconditions in vthe discharge side of the pump. A suitablemanual control is also provided upon the servomotor associated with the pump of the trans-mission.

The servomotors |00 and |00a` of the pump 9 and the motor 9a are of the type just described. The servomotor |00 has an automatic pressure control device |20 associated therewith consisting of a chamber |2| enclosing a'Sylphon bello'ws |22. The Sylphon bellows |22 has a plunger |23 extending therefrom which is 'connected' tothe control rod ||0 of the servomotor |00. A conduit |24 connects the discharge conduit 94 of the pump 9 with the interior of the chamber |2| so that .an-increase of pressure within the chamber |2| tends to collapse the bellows |22 againstKthe spring |25 to move the control rod ||0 in a downward direction and thus yshift the cylinder of the pump toward concentric position.

A manual control of the setting of Vthe eccentricity of the cylinderfor the pump 9 consists of |08 uncovers' the edge oi theV passage ||4 to permit fluid to flow to the right the pressure existing within a. lever |26 pivoted at |21 having one end thereof connected to the control rod I and the opposite end thereof in engagement with an adjusting screw |28. The adjusting screw |28 limits the upward movement of the control rod Ill as urged by the spring |25 to thereby regulate the eccentric position of the cylinder of the pumpl 9. Upward movement of the screw |28 causes downward movement of the control rod Ito decrease the eccentricity of the pump 9 while downward movement of the screw |28 permits upward move- 'mentof the control rod ||0 as urged by the spring |25 to thus limit the eccentric position of the pump 9. The spring |25 urges the ,bellows |22 to expand upwardly and thus cause the servomotor to retain the cylinder of the pump 9 upon eccentric position until the pressure in the conduits 94 and |24 is suiiicient to overcome'the force exerted by the spring |25, at which time the bellows |22 will be collapsed and thecontrol rod I I0 will be moved downwardly by means of the pressure against the action vof spring within the servomotor |00 to shift the cylinder toward neutral position. y

The power mechanism or electric motor |29 drives the pilot pump 45 since it is mounted upon the shaft 42 for the pump 9 whereby the pilot pump always supplies pressure to the servomotors |00 and |00a at any time the transmission is in operation. The operation of the system of Figure 6 is identical with the operation of the system of Figure so that the control mechanism of the pump 9 will operate either as a safety control only or as a constant torque control for the motor 9a.,

Having thus fully described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A hydraulic transmission comprising; a

, pump unit consisting of a cylinder, a rotor disposed within said cylinder and having a plurality of vanes movable therein and extending therefrom into engagement with the walls of said cylinder, spring means for moving said cylinder with respect to said rotor to position the same eccentrically thereto and place said pump unit on full stroke position, piston means opposing said spring means for moving said cylinder to place the same on `neutral stroke position, manual means for actuating said piston means and thus moving said cylinder to pre-set the position of the cylinder with respect to said rotor and control the volume delivery of said pump unit, a motor unit consisting of a cylinder, a rotor disposed within said cylinder and having a plurality of vanes movable therein and extending therefrom into engagement with the walls of said cylinder, spring means for moving said cylinder with respect to said rotor to position `the same eccentrically thereto `and place said motor unit on full stroke position, manual means opposing said spring means for moving said cylinder to pre-set the position of the cylinder with respect to said rotor and control the output speed thereof; means connecting said pump unit and said motor unit in a closed fluid circuit relationship; Ia pilot pump drivingly connected to said pump unit and oper.- ated concomitantly therewith, means regulating the maximum delivery pressure from said pilot pump means connecting the discharge side of said pilot pump with the under side of the vanes of said pump unit to retain the same in engagement with the cylinder wall thereof, said vanes of said pump unit having the ends thereof engaging the cylinder wall exposed to the pressure in said pump unit whereby said. vanes collapse against said pilot pump pressure to relieve excessive pressure conditions in said pump unit; and means for conducting fluid pressure from the discharge side of said pump unit to said piston means for applying hydraulic pressure thereon to actuate the same to overpower said pump unit spring means whenever the discharge pressure from the pump unit is greater than the force exerted by the pump unit spring means.

2. A hydraulic transmission comprising; a pump unit consisting of a cylinder, a rotor disposed within said cylinder and having a plurality of vanes movable therein and extending therefrom into engagement with the walls of said cylinder, spring means for moving said cylinder with respect to said rotor to position the same eccentrically thereto and place said pump unit on full stroke position, servomotor means opposing said spring means for moving said cylinder to place the same on neutral stroke position, a pilot pump drivingly connected to the pump unit adapted to be driven thereby whenever the pump unit is yin operation, means for regulating the maximum pressure produced by said pilot pump, means connecting said pilot pump to said servomotor for conducting iiuid to said servomotor for actuating the same, manual means for initiating actuation of said servomotor whereby said fluid from said pilot pump can complete actuation thereof and thus move said cylinder to pre-set the position of the cylinder with respect to said rotor and control the volume delivery of said pump unit; a motorunit consisting of a cylinder, a rotor disposed within said cylinder and having a plurality of vanes movable therein andextending therefrom into engagement with the walls of said cylinder, spring means for moving said cylinder with respect to said rotor to position the same eccentrically thereto and place said motor unit on full stroke position, said spring means for moving said cylinder to pre-set the position of the cylinder with respect to said rotor and control the output speed thereof; means connecting said pump unit and said motor unit in a closed fluid rcircuit relationship; and means connecting the discharge side of said'pump unit with said servomotor to apply the discharge pressure thereupon to overpower said pump unit spring means whenever the discharge pressure from the pump unit is greater than the force exerted by the pump unit spring means.

3. A hydraulic transmission comprising; .a pump unit consisting of a cylinder, a rotor disposed within said cylinder and having a plurality of vanes movable therein and extending therefrom into engagement with the walls of said cylinder, spring means for moving said cylinder with respect to said rotor to position the same eccentrically thereto and placel said pump unit on full stroke position, servomotor means opposing said spring means for moving said cylinder to place 'the saine on neutral stroke position including a power piston for actuating said cylinder and a control piston slidable within said power piston for valving ilui-d ilow to opposite ends of said power piston, a pilot pump drivingly'connected to the pump unit adapted to be driven thereby whenever the pump unit is in operation, means for regulating the maximum pressure produced by said pilot pump, means connecting said pilot pump to said servomotor for conducting fluid to said servomotor for actuating the same and for applying fluid pressure on one side of said power piston for always urging the same in one direcmanual means opposing tion, manual means for initiating actuation o! said servomotor whereby said fluid from said pilot Pump can complete actuation thereof and thus move said cylinder to pre-set the position of the cylinder with respect to said rotor andcontrol the volume delivery of said pump unit; va motor unit consisting of a cylinder, a rotor disposed withinsaid cylinder and'having'a plurality of vanes movable therein and extending therefrom into engagement with the` walls of said cylinder, spring means for moving said cylinder with respect to said rotor to position the same eccentrically thereto and place said motor uniton full stroke position, manual means opposing said spring means for moving said cylinder to pre-set the position of the cylinder with respect to said rotor and control the output speed thereof; means connecting said pump unit and said motor unit in a closed uid circuit relationship; and means operably connecting the discharge side of said pump unit with said servomotor to apply the discharge pressure thereupon to overpower said pump unit springmeans whenever the discharge pressure from the pump unit is greater than the force exerted by the pump unit spring means.

4. A hydraulic transmission comprising; a pump unit consisting of a cylinder,l a rotor disposed within said cylinder and having a plurality of vanes movable therein and extending therefrom into engagement with the walls of said cylinder, spring means for moving said cylinder with respect to said rotor to position the same eccentrically thereto and place said pump unit on full stroke position, servomotor means opposing said spring means for moving said cylinder to place the same on neutral position, manual means for moving said servomotor means and thus moving said cylinder to pre-set the position of the cylinder with respect to said rotor and control the volume delivery of said pump unit; a pilot pump drivingly connected to said pump unit foroperation therewith, means controlling the maximum pressure developed by said ,pilot pump, means connecting the discharge side of said pilot pump to said servomotor for power actuation thereof, means for conducting iluid pressure from said pilot pump to the underside of said vanes in said pump unit rotor to regulate the force applied upon said vanes maintaining them in engagement with said pump unit cylinder, a motor unit consisting of a cylinder, a rotor disposed within said cylinder and having a plurality of vanes movable therein and'extending Y therefrom into engagement with the wall-s of said cylinder, spring means for moving said cylinder with respect to said rotor to position the same eccentrically thereto and on. full stroke position, manual means opposing said spring means ormoving said cylinder to pre-set the position of the cylinder with respect to said rotor and control the output speed thereof; means connecting said pump unit and said motor unit in a closed fluid circuit relationship; said vanes of said pump unit having the ends thereof in engagement with the cylinder wall of said pump unit exposed to the pressure in said pump unit whereby -said vanes collapse against said pilot pump pressure to thereby relieve pressure in the compression, chambers oi said pump unit.

5. A hydraulic transmission comprising; a pump unit consisting of acylinder, a rotor disposed within 4said cylinder and having a plurality of vanes movable therein and extending therefrom into engagement with the walls of said cylplace saidmotor unit n inder, spring means for moving said cylinder with respect to said rotor to position the same eccentrically thereto and place said pump unit on full stroke position, servomotor means opposing said spring means for moving said cylinder to place the same on neutral position, manual means for moving said servomotor means and thus moving said cylinder to pre-set the position'of the cylinder with respect to said rotor and control the volume delivery `of rivingly connected to said pump unit for operation therewith, means controlling the maximum pressure developedby said pilot pump, means connecting the discharge side Vof said pilot pump to said servomotor for power actuation thereof', means for conducting iluid pressure from said pilot pump to the underside' of said vanes in said pump unit rotor to'regulate the force applied upon said vanes maintaining them in engagement with said pump unit cylinder, a motor unit consisting of a cylinder, a rotor disposed within said cylinder and having a plurality of vanes movable therein and extending therefrom into engagement with the walls of said cylinder, spring means for moving said cylinder with respect to said rotor to position the same eccentrically thereto and place said motor unit on full. stroke position, manual means opposing said spring means for moving said cylinder to pre-set the position of the cylinder with respect to said rotor and control the output speed thereof; means ccnnecting said pump unit and said motor unit in a closed fluid circuit relationship; said vanes of said pump unit having the ends thereof in engagement with the cylinder wall Vof said pump y unit exposed to the pressure in said pump unit wherebyA said vanes collapse against said pilot pump pressure to thereby relieve pressure in the compression chambers of said pump unit, and

means connecting the discharge -side of said pump unit with said servomotor to actuate the same to overpower said pump unit spring means when the discharge pressure from the pump unit is greater than Ythe force exerted by the pump unit spring means.

6. A hydraulic transmission compri-sing; a motor unit consisting of a cylinder, a rotor disposed within said cylinder having a plurality of vanes movable therein into engagement with the walls of said cylinder, means for vmoving said cylinder with respect to said rotor to position the same eccentrically thereto for regulating the output speed of said motor unit; a pump unit consisting of a cylinder,

a rotor disposed within said cylinder having an uneven number of vanes movable therein and extending therefrom into engagement with the walls of said cylinder, pilot pump means driven concomitantly with said pump unit and supplying fluid under pressure beneath the vanes thereof to hold them in engagement with the cylinder wall, a fluid inlet and a uid outlet in said cylinder disposed on diametrically opposite sides oi said rotor, land areas between said inlet and said outlet disposed on diametrlcally opposite sides of said rotor and from said inlet and said outlet, said land areas being of equal length,lspring means engaging said cylinder for positioning the same eccentric to said rotor; and means connectingr said pump unit and said motor unit in a closed nuid relationship; whereby said pump unit automatically reduces its stroke in response to the internal pressure developed within said pump unit means to urge vsaid position and thereby which opposes said spring cylinder to neutral stroke said pump unit; a pilot pump and extending therefrom s in `the pump unit.

' WARRimv R."11170112111` REFERENCES v'CITED l The following references are of record in the file of this patent: 1-

UNITED `stmluzs PATENTS p Number Name Date Manly -10ct; 30,l 1917 l Number' 115'v Number 16 Name lDite Douglas Oct. 8 1938 Thoma L,--' June 6,1939 `Von Saalfeld Feb. 22, 1916 Thomas j r Feb. 9,'1926 Rose Dec. 24, 1940 Robson Aug. '1, 1928 Ferris et al Sept. '18, 1934 Benedel:V Aug, 13,1940 Hamilla et al.. June 13,1933

Kendrick Sept. 16, 1941l Manly JulyV 26, 1921 FOREIGN PATENTS Country `Date lGerman Nov. 3, 1925 French Dec. 20, 1920 French July` 22, 1935 

